Baseball and softball bats, hereinafter referred to simply as “baseball bats”, are today typically made solely from aluminum alloys, or aluminum alloys in combination with composite materials (hybrid bats), or most recently solely from composite materials. Such bats are tubular (hollow inside) in construction in order to meet the weight requirements of the end user, and have a cylindrical handle portion for gripping, a cylindrical barrel portion for striking, and a tapered mid-section connecting the handle and barrel portions.
When aluminum alloys initially replaced wooden bats in most bat categories, the original aluminum bats were formed as a single member, that is, they were made in a unitary manner as a single-walled aluminum tube for the handle, taper, and barrel portions. Such bats are often called single-wall aluminum bats. More recently (in the mid 1990's), improvements in bat design largely concentrated on bat performance (such as increased hit distance). This has been accomplished primarily by designing the barrel portion of the bat with inner or internal, and outer or external, members; these members are often referred to individually as inserts, sleeves, bodies, shells or frames in the prior art. Such two member bats are often called double-wall bats. Each member is thinner than the single walls of the prior art bats.
The prior art double-wall bats generally refer to improved performance or hit distance as trampoline effect, slugging capacity, spring, compliance, lively, rebound, flexibility, etc. resulting from the double-wall two member construction allowing the barrel portion of the bat to deflect or flex more upon ball impact which propels the ball faster and further than single-wall bats. The main engineering principle, that is, bending theory, for such improved performance is not disclosed nor understood in the prior art. Thus, optimization of hitting performance is not achieved in the prior art.
U.S. Pat. No. 5,303,917 to Uke discloses a two member bat of thermoplastic and composite materials. Such bats made of one or more thermoplastic members have proven to have neither sufficient durability nor performance in actual play.
U.S. Pat. No. 5,364,095 to Easton discloses a two member bat consisting of an external metal tube and an internal composite sleeve bonded to the inside of the external metal tube making it in effect a single-wall bat. Since the two members cannot flex independently, this is not a high performance bat.
U.S. Pat. No. 6,322,463B1 to Chauvin discloses the method of tuning a unitary member all composite bat without separation barrier(s) making it a single-wall bat and thus not a high performance bat.
U.S. Pat. No. 5,415,398 to Eggiman discloses a two member metallic bat consisting of a frame and internal insert in a double-wall construction. Further U.S. Pat. Nos. 6,251,034B1 and 6,482,114B1 disclose variations to U.S. Pat. No. 5,415,398. U.S. Pat. No. 6,440,017B1 to Anderson also discloses a two member bat with an outer sleeve and inner shell.
U.S. Pat. No. 6,063,828 to Pitzenberger discloses a two member bat consisting on an internal body and an external shell in a double-wall construction. U.S. Pat. No. 6,461,760B1 to Higginbotham discloses the bat of U.S. Pat. No. 6,053,828 with a composite shell formed to an outer shell. As the composite is bonded to the outer shell this construction acts as a double-wall bat.
Similarly, U.S. Pat. No. 6,425,836B1 to Mizuno discloses a two member bat with a lubricated coating between layers or a weak boundary layer formed on the surfaces of the inner member. Such a bat may or may not act like a double-wall bat.
U.S. Patent Pub. 2001/0094882 A1 by Clauzin discloses a two member bat consisting of an outer shell and an insert laminate partially bonded to the shell.
While the prior art two member double-wall bats have demonstrated improved performance as claimed, the opportunity for further performance improvement is significant. Also, they provide inconsistent performance improvement along the barrel portion of the bat, and from bat to bat, due to lack of precision resulting from assembling the two unjoined members which invariably results in gaps along the joint. Further, they are very costly due to the multiple manufacturing steps, and this has resulted in a many-fold increase in end user costs.
Therefore, what is needed are single member or unitary double-wall and multi-walled bats which have equal or higher performance than the prior art, which are more consistent in performance, and which are significantly less costly to manufacture.